import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		
		int N = sc.nextInt();
		
		int sum = 0;
			
		for(int i = 1; i <= N; i++) {
			sum += i;
		}
		
		System.out.println(sum);

	}
}